Coaxial cable forming apparatus



Aug. 20, 1968 T. J. MOGEAN 3,397,442

COAXIAL CABLE FORMING APPARATUS Filed Nov. 12, 1965 6 Sheets-Sheet 1SIZING DEVICE FIG.

ADJUSTER INVENTOR 7. J. M GEAN ATTORNEY g- 968 "r. J. MOGEAN 3,397,442

COAXIAL CABLE FORMING APPARATUS Filed Nov. 12, 1965 6 Sheets-Sheet 2FIG. 3

Aug. 20, 1968 T. J. MCGEAN 3,397,442

COAXIAL CABLE FORMING APPARATUS Filed Nov. 12, 1965 6 Sheets-Sheet 5Aug. 20, 1968 T. J. MCGEAN 3,397,442

COAXIAL CABLE FORMING APPARATUS Filed Nov. 12, 1965 6 Sheets-Sheet 4 FIG.9

Aug. 20, 1968 T. J. M GEAN 3,39

COAXIAL CABLE FORMING APPARATUS Filed Nov. 12, 1965 6 Sheets-Sheet 5Aug. 20, 1968 A T. J. MCGEAN 3,397,442

COAXIAL CABLE FORMING APPARATUS FIG. [3 FIG. /4

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o I 2 a 4 5 o I 2 3 4 5 FORMER STAGE FORMER STAGE United States Patent O3,397,442 COAXIAL CABLE FORMING APPARATUS Thomas J. McGean, East Orange,N.J., assignor to Bell Telephone Laboratories, Incorporated, New York,N.Y., a corporation of New York Filed Nov. 12, 1965, Ser. No. 507,330 9Claims. (Cl. 29202.5)

ABSTRACT OF THE DISCLOSURE A transversely corrugated ribbon is shapedinto a tube by passing it between two radially adjacent rolls, one ofWhose peripheral edges has a concave profile and the other a convexprofile, to bend the ribbon transversely. The edges of succeeding pairsof radially adjacent rolls continue curving the ribbon transverselyabout a spacer-carrying center conductor until the ribbon surrounds thecenter conductor. The profile radius in the edges of each of thesuccessively arranged pairs is inversely proportional to the sequentialposition of the pair.

This invention relates to coaxial cable manufacturing apparatuses,particularly the portions of such apparatuses that advance a ribbon andbend it transversely about a spacer-carrying center conductor until itforms a tube-like outer conductor of an individual coaxial. Theinvention has for its principal object to bend transversely corrugatedribbons into corrugated outer conductors and thus make coaxials such asthose described in the copending application of M. C. Biskeborn et al.,Ser. No. 507,391, filed Nov. 12, 1965, assigned to the same assignee asthis application and being filed concurrently herewith.

Generally for forming of the coaxials such apparatuses fold the outerconductor about the center conductor by pulling a metal ribbon eitherthrough a conical die, or between pairs of rolls that are set up insuccessive stages and wherein the peripheral surfaces of the rolls ineach pair have concave profiles whose radii also decrease conically,that is linearly, from stage to stage. This operation is acceptable forforming smooth outer conductors from flat ribbons. However, if aresulting coaxial is to exhibit the advantageous flexibility and uniformelectrical stability available from corrugated outer conductors,additional expensive steps are necessary. For example, it is possible tocorrugate the smooth outer tube after forming it. Since this involveschanges in the inner diameter of the tube and the total tube length,this process has been found extremely difficult and may harm thedielectric spacers.

On the other hand, corrugating the ribbon prior to forming creates otherproblems. In particular, the forces pulling the corrugated ribbonthrough the conical die or the linearly decreasing profiles ofsuccessive roll pairs, which forces are normally insufficient to affecta smooth ribbon adversely, are sufficient to pull out the corrugationsin the ribbon. Attempts to allevate corrugation pull-out by multiplyingthe number of roll formers so as to change the ribbon curvatures onlygradually have failed to produce desired results. Also powering theindividual roll stages by turning them and thereby providing some of theforward force so as to alleviate the need for heavy pulling forcesresults in relatively complicated forming devices requiring strictcontrol and regulation of pulling speeds and roll speeds.

A general object of the present invention is to improve apparatuses ofthis type.

Another object of this invention is to wrap an elongated andtransversely corrugated ribbon across its length about a centerconductor and into a tube without complicating the forming device,particularly without applying power 3,397,442 Patented Aug. 20, 1968 iceto former rolls, while nevertheless maintaining the corrugations.

Yet another object of the invention is to form such a tube from acorrugated ribbon without pulling out the corrugations, whilenevertheless supplying the forming energy only by pulling on the tubeand ribbon.

According to the invention these objects are obtained not by making thecurving process more gradual with extra pairs of rolls but by making itmore acute, so that each pair bends the corrugated ribbon far more thangenerally considered feasible, thereby minimizing the number of rollstages and the necessary pulling force. This is done by drawingcorrugated ribbon between the peripheral surfaces of radially adjacentrolls in successive stages as previously, but imparting to theperipheral surfaces of each pair of rolls, profiles whose radii decreasenot linearly as in the past, but radii that decrease hyperbolically fromstage to stage. More particularly, according to the invention, theprofile in each stage adds the same amount of curvature to the ribbon.Preferably the number of stages is such that this constant curvature perstage is the maximum possible for forming the ribbon without bucklingit. The former then has the minimum number of stages necessary forforming the tube.

The invention is based upon the recognition that the usual practice oflinearly decreasing the profile radii comparable to the method of aconical die concentrates most of the forming work near the final rollstage. The invention is based on the further recognition that inaddition to the impedance of the rolls associated with formation of thetube, each roll pair imparts an impedance that is connected withrestoring the departure in shape from the shape imparted to it in theprevious roll stage due to the ribbons inherent elasticity and the workin overcoming the friction of the rolls against the ribbon arising fromdifferences in linear speeds along the roll surface, as well asovercoming the forces on the ribbon edges required to maintain theangular position of the partially formed tube. This involves, therefore,the recognition that multiplying the number of rolls increases the totaldecorrugating pull. It also involves the recognition that by bending theribbon the maximum amount possible at each stage the number of stages,and hence the above residual resistance is minimized.

Moreover, the invention involves the discovery that the bending limitsassociated with flat ribbons, contrary to appearances, are inapplicableto corrugated ribbons. Corrugated ribbons can be bent transversely farmore than flat ribbons. This is so because while a pair of rolls isbending the ribbon, the ribbon edges stretch longitudinally betweenentrance and exit of the pair of rolls so that if the degree ofcurvature is not limited the stretch edges may not be returnable totheir previous dimensions. This results in tubes having scalloped edgesalong the seams. On the other hand, corrugated ribbons are free fromthis source of distortion due to the ability of the corrugations toaccept considerable stretch and restoration.

The invention is based on the further discovery that the maximumcurvature that each stage can safely impart to a corrugated ribbon isapproximately the same. Thus, after the maximum change in curvature isestablished the number of rolls and the radii of the rolls can beestablished by making them impart the same change in curvature to theribbon. This involves linearly increasing the ribbon curvature ratherthan linearly decreasing the diameter.

The above and other features of the invention are pointed out in theclaims. Other objects and advantages of the invention will becomeobvious from the following de tailed description when read in light ofthe accompanying drawing wherein:

FIG. 1 is a schematic and block diagram of a forming operation thatproduces coaxials and embodies features of the invention;

. FIG. 2 is a perspective view of a roll former in FIG. 1;

FIGS. 3, 4, 5, 6, and 7 are end views of the rolls in the respectivesequential five 'staegs of the former in FIG. 2;

FIG. 8 is a perspective view showing details of a roll stage havingrolls with vertical axes and forming part of the structure in FIG. 2;

FIG. 9 is a perspective view showing details of a stage in FIG. 2 havingrolls with horizontal axes;

FIG. 10 is an elevation of a seam adjuster in FIG. 2;

FIG. 11 is an end view of a roll stage in FIG. 1 that assures anoverlapping edge on the corrugated outer conductor;

FIG. 12 is a cross section showing a coaxial manufactured according tothe invention by the apparatus of FIG. 1;

FIG. 13 is a graph illustrating the average curvatures of rolls as afunction of the stage; and

FIG. 14 is a diagram illustrating the cumulative force necessary fordrawing ribbon through the former at various stages.

In FIG. 1, showing a coaxial manufacturing apparatus according to theinvention, a roll former 10 continuously receives a longitudinallyadvancing ribbon 12 that has been transversely corrugated by passingbetween the peripheral teeth of two corrugating rolls 14. Also arrivingat the former 10 is a center conductor 16 coaxially carryinglongitudinally separated disc-shaped spacers 18 made of a dielectricmaterial. The center conductor 16 and the spacers emerge from a hollowplastic guide 20. Constituting the source of advancing power for theribbon 12, as well as the spacer-carrying center conductor 16, is a capstan 22 that pulls both of these when they have been combind to form thefinal coaxial 24.

The former 10 transversely wraps the longitudinally advancing ribbon 12about the spacers 18 on the longitudinally advancing center conductor 16until the ribbon takes the shape of a tube 26 having abutting edges thatform a longitudinal seam. An adjustor 28 through which the tube 26 isdrawn overlaps the seam edges. Creating the final diameter of the tube26 with the overlap edges is a sizing device 30 that forces the tube toassume its final size before guiding it to a solder device 32 forclosing the seam. A take up reel 34 stores the finished coaxial as itemerges from the capstan 22.

FIG. 2 illustrates the former 10, the adjuster 28, and the sizing device30, as well as their relations to each other in the apparatus of FIG. 1.In FIG. 2 a first forming, or roll stage 36 includes a top roll 38 whoseperipheral surface has a convex profile and a bottom roll 40 whoseperipheral surface has a concave profile of a diameter somewhat smallerto accommodate the corrugation depth of ribbon 12. The stage 36 bendsthe transversely corrugated metal strip or ribbon 12 that is beingpulled between the rolls from left to right by the capstan 22, toapproximately five times the diameter of tube 26. A second roll stage 42having a top roll 44 whose peripheral edge has a convex profile and aconcave-profile roll roll 46 further bends the horizontally pulledribbon 12 to the diameter of the tube 26'. Both of these first twostages start to shape the ribbon when the convex-profile top rolls 38and 42 exert a positive force to the center of the ribbon 12 while therolls 40 and 46 exert forces on the edges.

The stationary plastic tube 20 guiding the moving conductor 16surrounded by longitudinally separated discshaped spacers 18 feeds thecenter conductor onto the trough of the now-bent ribbon 12 as the ribbonpasses into the nip of two horizontally oriented and radially adjacentrolls 52 and 54 of a roll stage 56. The hollow profiles of theperipheral surfaces on the rolls 52 and 54 squeeze the edges of thesemicircular ribbon together to a radius substantially of the radius oftube 26. The

ribbon now carrying the center conductor 16 is drawn to a second stage58 of the horizontally oriented rolls 60 and 62. The profiles of theperipheral surface ino the latter two rolls 60 and 62 are both concavebut exhibit substantially' A; of the radius of tube26 for furthercompressing the sides of the ribbon 12. A pair of vertically orientedrolls 64 and 66 form part of a roll stage 68 and possess peripheralsurfaces with profiles of still greater curvatures, that is to say, theradius of tube 26. The ends of the peripheral surface force the edges ofthe ribbon together until they substantially abut. The ribbon nowconstitutes the tube 26. i

As stated, and according to the invention the profiles of the peripheralsurfaces on the rolls 38 and 40 in the first stage have a radiussubstantially five times the final radius of the tube 26, that is .tosay that the convex peripheral surface of roll 38 has a profile radiusof five times the radius of the tube 26 and the concave peripheralsurface of the roll 40 has a profile radius five times the desiredradius of the tube 26. Moreover, the succeeding stages have respectiveperipheral surfaces with respective profile radii and one times thedesired radius of the tube 26. Thus, the curvature of the profiles oneach roll increases from to to to to of the final curvature, i.e.,linearly from stage to stage. Generally each profile radius is n/s timesthe final radius r where n is the number of stages and s is the stagenumber.

If the final coaxial to be formed needs only a seam with abutting edgesthe tube 26 emerging from the former 10 is the final product. Theadjuster 28, the sizing device 30, and the soldering device 32 then canbe dispensed with. If the tube 26 with the abutting edge seam must besoldered, only the solder device 32 is necessary. However, Where theribbon 12 is laminar and the seam in the final product overlapped as inthe before-mentioned copending Biskeborn et al. application, theadjuster 28 and the sizing device 30 are also essential. In that case,the tube 26 passes into the adjuster 28. The latter includes a seampositioner 72. As the tube 26 is pulled the seam positioner 72 places aknife edge between the ribbon edges and partially depresses one edge. Anoverlap stage 74 having two horizontally adjacent rolls 76 and 78 whoserespective peripheral surfaces have different curvatures forces thedepressed edge under the other edge so as to properly initiate theoverlap.

Two horizontally adjacent rolls 80 and 82 form the first stage 84 of thesizing device 30. These rolls are sizing rolls and apply the marginalforce needed to close up the seam. The final sizing stage 86 iscomprised of two vertically aligned sizing rolls 88 and 90 which forcethe corrugated edges to nest inside each other and provide the tightjoint essential to proper soldering. I

The entire former 10, adjuster 28 and sizing device 30 rest on a base 92having horizontally-slotted rails 94. Each stage in the former 10,adjuster 28 and sizing device 30 includes a stand 96 which is movable'between the rails 94 but which is secured to the desired position bysuitable bolts 98. The nips of the rolls in the stages are all aligned.

FIGS. 3, 4, 5, 6, and 7 illustrate the rolls 38, 40, 44, 46, 52, 54, 60,62, 64, and 66 and their working relationship. Each roll has aperipheral forming surface S. The ribbon 12 appears between each pair ofrolls as they shape the ribbon. The forming surface S in the rollsterminates in ridges R against which the edges of ribbon 12 abut. Theridges R maintain the angular position of the ribbon. In stage 68 nosuch ridges exist because the ribbon edges abut against each other asthey pass through the rolls 64 and 66.

The stage 58 representing a typical s't-age having horizontally orientedrolls, that is rolls with vertical axes, appears in FIG. 8. Here thestand 96 comprises two T-blocks 100, both of which slide on two steelways 102 seated on a mounting platform 104 that rides between the rails94. Two hollow tubes 106' form bearing blocks cantilever-supporting theaxles 108 of the rolls 60 and 62. The hollow tubes 106 are threaded onthe outside into the T-blocks 100 and held by lock nuts 110. Knurledshoulders 112 permit vertical positioning of the rolls 60 and 62. Lockbolts 114 allow horizontal adjustment of the T-blocks 100 in the ways102 for purposes of providing proper clearance between the rolls 60 and62. The rolls 60 and 62 have horizontal fiat surfaces 115 which engagethe upwardly curving edges of the ribbon 12 so as to maintain theangular position of the ribbon and prevent it from twisting.

Details of the roll stage '68 representing a typical stage withvertically adjacent rolls are illustrated in FIG. 9. Here the rollerbearings are mounted in T-blocks 120 which can slide up and down on twocolumns 122 and 124 for adjustment of the roll height. The rolls 64 and66 are cantilevered off the T-rblocks. A knurled wheel 130 between theT-blocks 120 rotates a left-hand and righthand thread stud in the T-blocks to move the rolls apart ortogether so as to furnish an accurate,infinitely adjustable roll clearance. The columns 122 and 124 form partof a chair-shaped support 132 that rides between the rails 94.

FIG. illustrates the seam positioner 72 in detail. Here a verticallyoriented wheel 136 cantilevered out along a horizontal axis from a stand138 possesses a knife edge 140. An adjusting handle 142 turns a wormthat raises or lowers the bearing assembly 144 of the wheel 136 until itfits into the seam of the tube 26. In FIG. 10 the axial width of theknife edge has been exaggerated for clarity. Since the tube 26 haspreviously been oriented to place the seam at the very top, the knifeedge places a peripheral counterclockwise torque on the tube. The ribbonedge of the seam abutting the vertical portion of the knife edge 140 isthus continuously biased against this edge. The flat part 146 of thewheel 136 lightly depresses the underlap side.

The overlap rolls 76 and 78 on the stage 74 shown in detail in FIG. 11immediately take advantage of this depression and torque. The roll 78 onthe underlap side of the seam has a radius .014 inch smaller than theroll 76 on the overlap side. This results in a tube 26 whose overlappedside is .028 inch greater than the underlapped side shown in FIG. 12where the dimensions have been exaggerated for clarity. Thecounter-clockwise torque developed by the knife edge wheel 13 6preceding this pair of rolls assures driving of the overlap edge againstthe edge of the roll 78 whose peripheral surface has a profile with thesmaller radius. The thus displaced edges furnish assurance that theoverlapped tube will be formed to final size without crosslap.

The rolls 44 and 46 possess an additional detail necessary for assuringproper overlap of the tube edges and nesting of the corrugations. Onthese rolls, the profile of surfaces has an average radius equal to ofthe radius of the tube 26. However, the ends 150 of the profile formingthe edges of the ribbon 12 have radii slightly smaller than the averagewhile the radii of the center portion 152 are larger. The edge profilesblend in tangentially with the radii along the major central portion ofthe profile. In effect, therefore, the rolls 44 and 46 are multiradiusrolls. The purpose of the additional radius sections is to bend theedges of the ribbon 12 while a positive force could still be applied tothe interior of the ribbon. This overcomes any tendency on the part ofsucceeding stages to concentrate too much of their bending energy in themajor central area of the ribbon and leave the edges of the ribbonflatter than they ought to be. The term average radius is used herein inthe sense that the smaller curvature along the center portion isweighted more heavily, i.e., proportional to the ribbon surface itoperates on, than the larger curvature of the ends 150.

For holding the tube 26 at the best soldering angle the entire assemblyof FIG. 2 may be rotated about its longitudinal axis.

In operation the capstan 22 pulls the tape 12 through the corrugatedrolls 14 and through the first two stages 36 and 42 which respectivelyimpart curavture to the tape 12 whose radii are respectievly five timesthe radius of the tube 26 and times the radius of the tube 26. A tube 20feeds a center conductor 16 carrying spacers 18 into the thus formedtrough. The roll stage 56 curves the ribbon 12 inwardly to a radiusequal-to times the radius of the tube 26. The succeeding stages 58 and68 further decrease the ribbon radius to values equal to and one timesthe radius of the tube 26. The capstan continues pulling the tube 26past the knife edge Wheel 136 which places sufficient torque onto thetube 26 so that when the latter enters the nip between the rolls 76 and78 as shown in FIG. 11 an overlap and underlap can be obtained. Withoutthis torque the right edge of the tube 26 shown ing FIG. 11 may enterthe left-hand roll 76.

The overlapping stage 84 and the sizing stage 86 finish the tubesufiiciently to allow it to pass to the solder device 32 after which thefinished tube can be taken up on the reel 34.

The invention achieves the notable result of forming a coaxial having acorrugated outer conductor with a passive forming device requiring onlylongitudinal pull. By virtue of the radii of the profile of theperipheral surface on the rollers in each successive stage decreasinghyperbolically, that is with linearly increasing curvatures, the numberof stages is markedly decreased from that which would be necessary forforming noncorrugated tubing according to the principle which followedthe linearly decreasing radius of a conical die. The invention is basedupon, and the notable achievements thereof are based upon, recognitionof several factors which are to some extent interdependent. Theinvention involves the recognition that the capstan 22 pulling theribbon 12 must overcome not only a considerable work force that goesinto plastically bending the metal and forming it, but must overcome asubstantial drag due to such factors as the friction developing out ofthe different peripheral speeds along the profile of any one rotatingroll, the frictional force of maintaining the tube in one angularcontrol position, and the force necessary to return the ribbon to thedimension to which the previous stage had bent it and from which itresiliently departs. Such force may account for 30 to 40 percent of theforce necessary to pull the ribbon through the former. To minimize theseeffects the invention reduces the number of forming stages.

The invention is also based on the recognition that the reduction informing stages can go far further for corrugated ribbon thanuncorrugated ribbon and that each I stage can perform more work actuallyinvolved in plastically forming the tube than is possible with flatribbons. This is based upon the further recognition that the limit towhich flat ribbons can be formed transversely is defined by theirability to stretch at the edges when passing through rolls. Each ribbonwhen it passes through rolls has one form at the entrance and one format the exit. From entrance to exit the shape at the middle does notchange. However, the ribbon stretches at the edges in order to achieveits desired curvature. This stretching can be sufficient to prevent theribbon edges from being returned to their normal dimensions. Scallopedseams occur in the final product. This defect in normal ribbon issometimes overcome by placing an additional drag upon the ribbon beingfed into the rolls and increasing the pull on the ribbon. This has theeffect of actually drawing out the ribbon across its entire crosssection and constitutes a drawing operation. The extra pull would pullout corrugation and thus be unsuitable for corrugated conductors. Thus,while ordinary formers are unsuitable for forming corrugated coaxials,the formers ac- 7 cording to the invention may similarly be unsuitablefor forming smooth outer conductors.

The apparatus of FIG. 1 Was used to fold a tube 26 from a startingribbon 12 of .003" X 1.25" copper aligned at one edge with .010" X 1.375No. 1 temper tin-plated steel, and bonded thereto with Du Pont Alathon80F copolymer.

The five stages of former 28 each impart one-fifthof the totalcurvature. This number of stages is necessary for forming the tube 26from the before-mentioned ribbon unless each stage could impartone-fourth of the curvature without buckling the ribbon, in which case afour stage former would be possible. Stages capable of performingintermediate amounts of curving, i.e., between one-fifth and one-quarterof the final curvature, still establish the number of stages as fivebecause there can be no stage numbers between four and five.Nevertheless, these intermediate values indicate that tolerances on thevalues of the profile radii are possible. In fact that onefourth totalcurvature represents a limit that can be placed upon departures from therequirement that the curvatures imparted by each stage must be equal toone-fifth. This maximum tolerance would occur if for example four stagesimparting equal curvatures to the ribbons were almost, but not quite,sufiicient for forming the tube 26. Thus, the differences in curvaturebetween the profile radii from stage to stage in a five stage formercannot be greater than one-fourth of the total curvature.

This concept can be paraphrased for a general case. For ann-stage'former having a final radius of r, and a final curvature l/r,whose rolls in successive stages have actual profile radii of R and Rthe diiferences in curvature between successive stages, namely,

must be less than the share of the final curvature to be imparted by onestage in an ideal former having one stage less than n. The share foreach stage in an (nll)-stage ideal former is times the final or totalcurvature 1/r. Each stage must also produce some curvature. Thus,

This formula represents the maximum stage-to-stage departure permissiblefrom the rule that each stage adds the same curvature to the ribbon.

Moreover, it is possible within this tolerance to determine the possiblemaximum and minimum for the profile radius in each stage of an n-stageformer. The profile radius in any stage, which ideally is n/s times thefinal radius r, can reach down to a minimum value (when it would do themost bending) equal to an ideal stage in an (n1)-stage former, namely,reach down to It can reach up to a value where the other stages allfollow the (n1) stage ideal former radii of elm.

and the stages in question merely repeat the previous stage (s1),namely, reach up to a radius (n 1 )1 1 This may be stated in terms oftolerances, i.e., departures from the desired values of Thus, in eachstage the actual profile radius may exceed In each stage the profileradius may be less than Forming Roll Stage Roll Diameter Profile Radiusin Inches 1 Average value.

The results of forming the cable 24 at these dimensions is illustratedin FIG. 13. This diagram illustrates the linear increase in curvaturefrom stage to stage. FIG. 14 illustrates the cumulative force necessaryto draw the ribbon through the stages.

While an embodiment of the invention has been described in detail, itwill be obvious to those skilled in the art that the invention may beotherwise embodied without departing from its spirit and scope.

What is claimed is:

1. A roll former for shaping a transversely-corrugatedlongitudinally-pulled ribbon into a tube, comprising a plurality ofsequentially arranged roll stages each having two radially-adjacentfreely-rotatable rolls between which a corrugated ribbon can be pulled,said rolls in each stage having peripheral forming surfaces with curvedforming profiles spaced close enough to each other to bend the advancingribbon transversely, the peripheral surface in one roll of each of saidsequentially arranged stages having a concave forming profile, saidconcave forming profiles having respective average profile radii, theperipheral surface of the other roll in one of said sequentiallyarranged stages having a convex profile, the peripheral surfaces in theother roll of another later one of said sequential stages having concaveprofiles, the average profile radius in the first of said successivestages being substantially as many times greater than the final desiredradius as the number of stages, the average profile radius in each ofsaid successively arranged stages being substantially inverselyproportional to the sequential position of each stage with the averageprofile radius of the final stage having the desired final radius,whereby said stages can bend said corrugated ribbon passing between therolls to lesser and lesser diameters.

2. A roll former as in claim 1, wherein the profile radii in each stagesubstantially contact the entire width of said ribbon.

3. A roll former as in claim 1, wherein the profile radii in each stagesubstantially contact the entire width of said ribbon, and wherein saidrolls possess peripheral stops at the edges of said ribbons.

4. A device as in claim 1, wherein one of the stages with both convexand concave surfaced rolls has a multiradius profile with edges having asmaller profile radius than the remainder of the profile, said smallerprofile radius being substantially equal to the profile radius of thelast stage in said former.

5. A roll former as in claim 1, wherein the profile radii havetolerances in their values limited in that differences between thecurvatures of the forming profiles of said peripheral forming surface ofadjacent stages is less than the difference in profile curvaturesbetween adjacent stages in an otherwise identical former whose profileradii varied inversely with the stage position but which had one lessstage and without any tolerances.

6. A former as in claim 5, wherein the differences between profile radiiin adjacent stages is less than the final radius times the reciprocal ofone less than the number of stages.

7. A former as in claim 5, wherein the profile radius of each stage is8. An apparatus for forming coaxial cable from a transversely corrugatedribbon and a spacer-carrying center conductor comprising capstan meansfor longitudinally pulling said ribbon, a plurality of sequentiallyarranged roll stages each having two radially-adjacent freely-rotatablerolls applying force to the ribbon as it is being pulled, said rolls ineach stage having peripheral forming surfaces with curved formingprofiles spaced close enough to each other to bend the pulled ribbontransversely, the peripheral surfaces in one roll of each of saidsequentially arranged stages having a concave forming profile, saidconcave forming profiles having different respective average profileradii, said peripheral surface of the other roll in one of saidsequentially arranged stages having a convex profile, the peripheralsurfaces in the other roll of another later one of said sequentialstages having concave profiles, the average profile radius in the firstof said successively arranged stages being substantially as many timesgreater than the last as the number of stages, the average profileradius in each of said successively arranged stages being proportionalto the sequential position of the stage, the profile radius of the finalof said stages being equal to the desired final radius, whereby saidstages bend the corrugated ribbon passing between said rolls to lesserand lesser diameters, and means for guiding the spacer-carrying centerconductor into the trough formed in said ribbon after said stage havingsaid roll with a convex profile.

9. An apparatus as in claim 8 further comprising adjusting means betweensaid capstan means and said roll stages for overlapping the edges of theseam formed on said tube, and sizing rolls for producing a final overlapdiameter.

References Cited UNITED STATES PATENTS 2,156,934 5/1939 Barrett 29-20252,156,952 5/1939 Morsing 29-2025 X 2,764,214 9/1956 Reynolds et al.72176 3,026,924 3/ 1962 Lunt et a1. 29-202.5

THOMAS H. EAGER, Primary Examiner.

2% UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,397,4 2 Dated August 2O 1968 Iuventofls) Thomas MC G an It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 9, line 2 L, after "is" insert --between--;

line 28, delete "or" and insert --a.nd--,- lines 29 and 30, the formulashould be (SEAL) Attest:

a mum mm: E. mm, JR. Ed It. Gomissione'r at m Atteoting Officor

